Improving the Multi-Channel Hybrid Data Dissemination System

A major problem with the Internet and web-based applications is the scalable delivery of data. Lack of scalability can hinder performance and decrease the ability of a system to perform as originally designed. One of the most promising solutions to this scalability problem is to use a multiple channel hybrid data dissemination server to deliver requested information to users. This solution provides the high scalability found in multicast, with the low latency found in unicast. A multiple channel hybrid server works by using a push-based multicast channel to deliver the most popular data to users, and reserves the pull-based unicast channel for user requests and delivery of less popular data.The adoption of a multiple channel hybrid data dissemination server, however, introduces a variety of data management problems. In this dissertation, we propose an improved multiple channel hybrid data dissemination model, and propose solutions to three fundamental data management problems that arise in any multiple channel hybrid scheme. In particular, we address the push popularity problem, the document classification problem, and the bandwidth division problem. We also propose a multicast pull channel to the common two-channel hybrid scheme. Our hypothesis that this new channel both improves scalability, and decreases variances in response times, is confirmed by our extensive experimental results. We develop a fully functioning architecture for our three-channel hybrid scheme. In a real world environment, our middleware is shown to provide high scalability for overloaded web servers, while keeping the response times experienced by clients at a minimum. Further, we demonstrate that the practical impact of this work extends to other broadcast-based environments, such as a wireless network

Value in Experience. Design and Evaluation Framework based on Case Studies of Novel Mobile Services

The concept of ‘value’ has received extensive interest in research in the fields of psychology, marketing and, more recently, human-computer interaction (HCI). Gaining insights into users’ personal values can lead to a better understanding of user behaviour. However, the concept of value is not clearly defined, and researchers have produced differing views on the conceptualization of the construct. In the past decade, user experience has received considerable attention in HCI research. Yet the relationship between user experience and value has not gained much attention. The goal of this dissertation is to better understand and articulate the value in user experience. The focus is on novel mobile service solutions, taking into account the viewpoint of different user groups. Achieving an understanding of different user groups will greatly help design successful mobile services for target user populations. The empirical foundation for this dissertation is findings concerning user experience from seven individual case studies conducted in the field with the endusers. Interpretive case studies of novel mobile services in varying usage contexts involved different user groups: children, teenagers, college students and vision and memory -impaired older people. An initial value framework is developed as a synthesis from the literature. By utilizing this framework, the user experience findings obtained are re-examined from the point of view of value through a crosscase analysis and synthesis. Based on this analysis, value parameters from individual mobile service case studies are interpreted and categorized. The initial value framework is complemented by relying on the value parameters identified from the case studies. This work contributes to the field of HCI by showing that user experience and value are closely intertwined. The thesis proposes the concept of “value in experience (ViE)”, which refers to the user’s iterative (subconscious and conscious) interpretation and evaluation of user experience with a service. A value design and evaluation framework is presented and demonstrated by evaluating value in experience from the case studies. Also the designer values are analysed and compared with the value in experience. The framework presents a rich description of value dimensions relevant to specific user groups and mobile service domains in varying usage contexts. Furthermore, value in experience design and evaluation guidelines related to different user groups are proposed. The proposed conceptualization of value in experience offers insights to help understand the dimensions of value, and serves as a lens to guide interpretive analysis of value in experience. The complemented value design and evaluation framework is a tool for identifying and describing the key value dimensions for value in experience evaluation. Furthermore, the framework can support service design processes. The cross-case study findings provide insights into the special characteristics of different user groups and their value priorities in specific service domains. Even though the framework is based on mobile services, its main constructs are expected also to be applicable to other types of digital services